1. Field
The present invention relates to a substantially defect-free germanium wafer for use in a semiconductor device and in particular, to semiconductor devices comprising a substantially defect-free germanium wafer bonded to a silicon containing substrate without the need of an intermediate layer. The present invention further concerns the methods for making and using such devices.
2. Discussion of Related Art
There is increasing interest in using silicon-germanium (Sixe2x80x94Ge) alloy as a material for microelectronic and optoelectronic device applications. Germanium (Ge) is known to have high carrier mobility (e.g., high hole and electron mobility) and optical absorption as compared to silicon (Si). This is one reason why Ge is useful for devices that require enhanced performance and/or high quantum efficiency. Examples of devices that would benefit from the use of a Ge film include metal-oxide-semiconductor (MOS) transistors, optical detectors, and other optoelectronic devices, to name a few.
Forming high quality germanium layers on a substrate is desirable. Ge layers grown on a Si substrate can be used to make high mobility devices. Bulk Si substrates typically have lower electron and hole mobility than Ge substrates. Si typically has an electron mobility of 1500 cm2 N/s and a hole mobility of 450 cm2 N/s whereas Ge has an electron mobility of 3900 cm2 N/s and a hole mobility of 1900 cm2 N/s. Additionally, electronic devices made using bulk Si substrates require high power consumption due to current substrate leakage, especially for high performance devices. The lower mobility and the current substrate leakage problem in using bulk Si for substrate set upper limits on the performance of the electronic devices with regard to material and power dissipation aspects. On the other hand, electronic devices made with Ge require less voltage bias to turn on the devices because of the Ge""s high mobility characteristic. In addition, the use of the banded Ge to Si substrate allows the use existing infrastructure for Si substrate.
In the current art, electronic devices have been fabricated on Si substrate with a Ge film grown on an intermediate buffer layer (e.g., SiGe buffer layer) (e.g., through chemical vapor deposition). There is a large lattice-mismatched of about 4% between the Ge and the Si making the growing of the Ge film on a Si substrate to contain crystalline defects such as mistfit dislocations and high stress, which subsequently forms threading segments that penetrate the entire epitaxial layer and terminate at the free surface. The defect is even higher for thinner Ge film and thinner Ge films are desirable for many devices.
Defects in the germanium layer in a Sixe2x80x94Ge alloy are undesirable since they reduce Ge""s carrier mobility, and adversely affect the electronic quality and performance reliability of various electronic devices. And, bonding of a Ge wafer directly a Si wafer have not been successful because such bonding suffers from other defects such as thermally induced slip, bonding voids, unstable or weak interface and crystalline defect.